/**
 *    Copyright 2009-2015 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor;

import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.factory.ObjectFactory;
import org.apache.ibatis.session.Configuration;

import java.lang.reflect.Array;
import java.util.List;

/**
 * @author Andrew Gustafson
 */
/**
 * 结果抽取器
 */
public class ResultExtractor {
	/**
	 * 配置
	 */
	private final Configuration configuration;
	/**
	 * 对象工厂
	 */
	private final ObjectFactory objectFactory;
	/**
	 * 初始化
	 * @param configuration
	 * @param objectFactory
	 */
	public ResultExtractor(Configuration configuration, ObjectFactory objectFactory) {
		this.configuration = configuration;
		this.objectFactory = objectFactory;
	}

	/**
	 * 通过列表提取对象
	 * 
	 * @param list
	 * @param targetType
	 * @return
	 */
	public Object extractObjectFromList(List<Object> list, Class<?> targetType) {
		Object value = null;
		if (targetType != null && targetType.isAssignableFrom(list.getClass())) {
			// 1.如果targetType是list，直接返回list
			value = list;
		} else if (targetType != null && objectFactory.isCollection(targetType)) {
			// 2.如果targetType是Collection，返回包装好的list
			value = objectFactory.create(targetType);
			MetaObject metaObject = configuration.newMetaObject(value);
			metaObject.addAll(list);
		} else if (targetType != null && targetType.isArray()) {
			// 3.如果targetType是数组，则数组转list
			Class<?> arrayComponentType = targetType.getComponentType();
			Object array = Array.newInstance(arrayComponentType, list.size());
			if (arrayComponentType.isPrimitive()) {
				for (int i = 0; i < list.size(); i++) {
					Array.set(array, i, list.get(i));
				}
				value = array;
			} else {
				value = list.toArray((Object[]) array);
			}
		} else {
			// 4.最后返回list的第0个元素
			if (list != null && list.size() > 1) {
				throw new ExecutorException(
						"Statement returned more than one row, where no more than one was expected.");
			} else if (list != null && list.size() == 1) {
				value = list.get(0);
			}
		}
		return value;
	}
}
